Absorbed doses for internal radiotherapy from 22 beta-emitting radionuclides: beta dosimetry of small spheres

We calculated the mean absorbed fractions, specific absorbed fractions and mean doses per unit of cumulated activity in source spheres 10 μm-2 cm in radius for 22 beta-emitting radionuclides potentially useful in radioimmunotherapy. We considered two models of radionuclide distribution, either uniform at the surface of the source or throughout its volume. For each model, we calculated both the absorbed fractions in the spherical segments composing the source and the mean absorbed fractions. For surface distribution, we calculated the mean dose per unit of cumulated activity for a concentric sphere with a small radius (5 μm) in order to determine the minimal dose delivered to the target. Calculations were performed using point kernels for monoenergetic emissions and then integrated into the beta spectra of the different emitters (32P, 33P, 47Sc, 67Cu, 77As, 90Y, 105Rh, 109Pd, 111Ag, 121Sn, 131I, 142Pr, 143Pr, 149Pm, 153Sm, 159Gd, 166Ho, 177Lu, 186Re, 188Re, 194Ir and 199Au). Monoenergetic emissions were taken into account. (author)